A conventional testing device includes a testing circuit board electrically coupled to a testing machine and a signal transmission board disposed on the testing circuit board. The signal transmission board of the conventional testing device is soldered onto the testing circuit board. However, in the soldering process of the signal transmission board and the testing circuit board, the conventional testing device is easily damaged by thermal shock. Moreover, the signal transmission board and the testing circuit board fixed to each other by soldering are inconvenient for subsequent inspection and repair.